Estimate solar loads through glazing and opaque surfaces. Compare shading, orientations, materials, and cooling impacts. Build clear, printable engineering reports for informed decisions.
Glazed area excludes the frame fraction. Surface irradiance combines direct beam, sky diffuse, and ground-reflected radiation.
Solar Heat Gain Coefficient describes the fraction of incident solar energy that eventually enters a conditioned space through glazing. It includes directly transmitted radiation and the inward-flowing part of energy absorbed by the glass. A value near 0.25 admits much less solar heat than a value near 0.70. Lower values are often useful in hot climates or on exposed east and west façades. Higher values can support passive winter heating where seasonal solar access is desirable. SHGC differs from visible transmittance, which describes daylight rather than heat. Products can provide similar daylight while creating very different cooling loads.
SHGC addresses solar radiation. U-value addresses heat transfer caused by indoor and outdoor temperature differences. A window may have excellent insulation but admit substantial solar energy when its SHGC is high. A tinted product may reduce solar gain while still conducting heat if its U-value is poor. A complete assessment therefore considers both properties. Frame area matters because frames behave differently from center glass. This calculator removes the entered frame fraction from the solar-transmitting area while applying conduction across the full assembly area.
South-facing surfaces in the northern hemisphere often receive strong midday radiation, yet overhangs can control high summer sun effectively. East glazing tends to create morning peaks. West glazing often creates difficult late-afternoon loads when outdoor temperatures are also high. North façades receive more diffuse radiation and less direct beam under many conditions. Roofs and skylights can receive intense exposure for long periods because their tilt faces more of the sky. Azimuth identifies compass direction, while tilt identifies slope from horizontal.
Direct normal irradiance is measured perpendicular to the sun’s rays. Diffuse horizontal irradiance comes from the sky after atmospheric scattering. Global horizontal irradiance combines projected direct radiation with diffuse radiation. A tilted building surface receives a different mixture. The calculator projects direct beam onto the surface, estimates sky diffuse radiation, and includes ground-reflected energy using the selected albedo. Snow, pale paving, and bright nearby roofs can increase reflected radiation.
Exterior shading blocks solar energy before it reaches the glass and is normally more effective than interior shading. Interior blinds and curtains reduce the portion reaching occupied space, but absorbed heat remains indoors. Fixed overhangs work best when geometry matches the seasonal solar path. Side fins help with low-angle sunlight arriving from the side. Trees and neighboring buildings can provide shade, although their effect changes by season and hour. The geometric model here is simplified; complex obstructions require a detailed shadow study.
Solar radiation heats opaque exterior surfaces above ambient air temperature. Sol-air temperature represents an equivalent outdoor temperature including absorbed sunlight and longwave exchange. Dark finishes with high absorptance can become much hotter than light reflective finishes. Roof color is especially important because roofs receive strong exposure. Thermal mass delays and smooths heat flow, so the mass factor is an adjustment rather than a full transient simulation.
The selected-hour result checks a particular design condition. The hourly curve shows when solar and conductive components combine to produce the greatest load. Daily energy integrates half-hour values and helps compare alternatives. Monthly and annual outputs multiply the design-day result by equivalent days selected by the user. They do not replace a full weather-file simulation. Annual decisions should include typical meteorological data, equipment performance, occupancy schedules, infiltration, ventilation, internal gains, and controls.
Use manufacturer-rated whole-product SHGC and U-values whenever available. Center-of-glass values may understate frame and edge effects. Confirm whether ratings use metric or imperial units. Weather data should represent the location and design objective. For peak HVAC sizing, use recognized design conditions rather than an unusually mild day. Measure overhang projection, vertical gap, window dimensions, and façade direction carefully. Small azimuth errors can materially affect east and west windows.
This calculator provides engineering estimates. It does not automatically include people, lighting, appliances, ventilation, infiltration, duct gains, humidity removal, thermal bridges, or equipment diversity. It uses a simplified clear-sky method rather than a certified building-energy engine. Final HVAC capacity should use applicable standards, local code requirements, validated weather data, and qualified professional review. Avoid oversizing from one solar result because oversized systems may cycle poorly and manage humidity less effectively.
Important Note: All the Calculators listed in this site are for educational purpose only and we do not guarentee the accuracy of results. Please do consult with other sources as well.